Hi! I have a D750 and a D850 recently acquired. In my opinion, D850 has a wonderful performance in colour, focus and ISO, above other cameras. It's very fast. I love it! And the weight of the camera's body is not too much to carry in weddings. But the files are very heavy in the Large Raw format. You have to take that in mind in order to keep big hard drives and fast memory cards. I usually carry the two cameras. In Medium Raw at low lights it works similar or a little worst than in the D750 but it keeps very good colours and quality, with the same size of files than the D750. Hope this information helped you! The photo I attached is made with 50mm 2.2f 400/sg

David, d750 is more than enough to shoot weddings. If you are planning on shooting video, d850 has awesome newer and higher capabilities. On the other hand, D810 is just in between, that’s what I’ve been shooting with and looove it.